I'd say that the best way to troubleshoot any I2C\SPI problem is to use a DSO and capture the signals on both the clock and the data line. If you don't have a DSO then that makes things a hell lot difficult.


In case you don't have a DSO, I suggest that you write a program that modify\read the EEPROM not at the Power-fail but in a loop. Write a dummy data say 0x55 or oxAA (good numbers for troubleshooting most problems because of alternate 1s and 0s). Then read the same location and check put it on the display. From the value read back you "may" be able to identify the problem, whether it is a timing issue or a hardware problem.